In the pharmaceutical, building materials and food industries, on vessels and silos, on platforms and dosing systems, right around kitchen and bathroom scales ? weight is measured everywhere. In industry, it becomes particularly interesting when it comes to the level in vessels. There are numerous possibilities for weight measurement or weighing. The filling level could be determined optically, hydrostatically, by ultrasound, microwaves and radar, mechanically, capacitively, by heat dissipation, by displacement and resistance or, what this article is about, gravimetrically.
The term gravimetric comprises the Latin ?gravitas? for ?gravity? and Quick ??? ??????? for ?measure?. In gravimetric measurement, therefore, the heaviness of the mass is combined with the weight force to form a meaningful value and thus the level depends upon weighing vessels (the filling level results from the density of the medium and the geometry of the vessel). This makes gravimetric level measurement a part of weighing technology.
Gravimetric level measurement is particularly suitable when uneven distribution may appear within the vessels.
Gravimetric level measurement: Advantages
This kind of weighing has several advantages. Perhaps the greatest advantage is that the force transducers used for gravimetric level measurement are located beyond your vessel. Thus, they do not come into contact with the product. Nor is it necessary to open or modify the vessels. Contamination can thus be eliminated. Cleaning is also easier. Furthermore, very precise measurement is possible ? 0.02 % of the rated load isn’t uncommon with regards to relative linearity error. This makes dosing possible when, for instance, food is filled into bags ? and of course the packaging must contain the amount specified.
Another advantage is that the merchandise will not influence the measurement. The particular level can be determined gravimetrically for several contents ? solids, liquids, viscous substances, foaming substances ? even toxic or aggressive contents can be viewed as. Furthermore, the measurement isn’t falsified even if voids or uneven contents distribution occur inside the silo or tank, as the entire contents are weighed.
Suitable mounting modules not merely ensure that the weight force is properly led in to the force transducers, in addition they make installation super easy. The module and force transducer have a minimal height and a small installation volume. However, it can be problematic if the vessels already are permanently installed and will only be positioned on modules with significant amounts of effort. Then it is probably advisable to bolt strain transducers to the supports. Any risk of strain transducers determine the compression of the supports due to the weight of the contents. They thus be able to weigh immovable vessels gravimetrically.
Gravimetric level measurement: Disadvantages
The disadvantages of gravimetric level measurement vary in significance according to the application. Results are mainly distorted when force shunts can’t be prevented. Ideally, the vessel should be mechanically decoupled. Used, however, it could always happen that, for example, struts are absolutely necessary. Then it depends on how great their supporting effect is. Similar problems may appear if the measurement is influenced by a high bearing weight. The low the weight of the vessel when compared to product, the more accurate the gravimetric measurement. Finally, free-standing outdoor vessels could be suffering from natural factors. For instance, if wind pushes or snow leads to a significant increase in weight.
Typical force transducers for the weighing of vessels
Single point load cells are classically useful for scales. These not merely have a low price and high accuracy, however the weight is also determined reliably, no matter where it is positioned on the platform. For optimal force introduction, bending or shear beams with the corresponding weighing modules are often installed under tanks, silos or vessels that stand on supports. To determine the rated load of these force transducers, divide the full total weight of the vessel by the number of supports. If the rated load exceeds 10 t, you’ll be able to switch to compression force transducers, the utmost capacity of which reaches around 300 t. With four supports, vessels of up to 1,200 t could be weighed with the best accuracy. Alternatively, vessels can be suspended from S-type force transducers or fitted with strain transducers.
Note
Level could be measured in many various ways. Whether gravimetric as described, or with a submersible pressure sensor, float switch or pressure sensor ? WIKA gets the right sensor for every application. Do you want to buy the products? Inside our WIKA online-shop you will discover a few of our standard designs. Assuming you have any questions, your contact will gladly help you.
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